1. Field of the Invention:
This invention relates to a multiple glazed unit.
2. Discussion of the Prior Art and Technical Problems:
In general, multiple glazed units of the prior art include a desiccative spacer mounted between glass sheets or panes to provide an airspace therebetween. A moisture-impervious sealant seals the glass sheets and spacer to prevent moisture from moving into the airspace. A metal channel may be mounted on the peripheral and outer marginal edge portions of the glass sheets to protect the edges of the glass sheets and provide additional structural stability. It has been observed that the spacer of the prior art multiple glazed units may sag and/or bow after the units are in service. The term "spacer sag" as used herein is defined as displacement of the spacer toward the airspace. The term "spacer bow" as used herein is defined as displacement of the spacer away from the center of the airspace. The term "displacement of the spacer" and "spacer displacement" as used herein refers to "spacer sag" and/or "spacer bow".
When spacer sag occurs, the spacer moves into the vision area of the unit and detracts from the aesthetic appeal of the unit. In the instance where a metal channel is employed and/or the unit is mounted in a glazing system, spacer bow may cause chipping and flaking of the sharp, raw-cut glass edge as the spacer moves past the glass edge. This is attributed to edge pressure exerted by the channel and/or glazing system. As is well known in the art, glass edge damage weakens the glass sheets causing them to fracture. This is especially true when the glass sheets are heat absorbing and/or have a heat absorbing coating. Repeated spacer displacement, in addition to the above drawbacks, can rupture the moistureimpervious seal allowing moisture to move into the airspace. When this occurs, the desiccative spacer becomes saturated with moisture, and the excess moisture condensing on the inner surfaces of the glass sheets detracts from the aesthetic appeal of the unit; impairs the view of observer and reduces insulating properties of the unit.
Metal washers mounted on the peripheral edge portions of the glass sheets and a metal screw passing through the hole of the washer into engagement with the spacer, i.e., metal clips, have been employed to prevent spacer sag. Although the use of metal clips tend to reduce spacer sag, there are limitations. More particularly, as the spacer sags, the washers are urged against the edges of the glass sheets which can cause chipping and subsequent weakening of the glass edge portions. Another limitation is that the metal clips do not prevent spacer bow because the screw merely passes through the hole in the metal washer when the spacer bows.
Although the mechanism(s) that cause(s) spacer sag and/or spacer bow is(are) not completely understood, many theories are postulated. One of the mechanisms that is believed to cause spacer sag is change in atmospheric pressure. When atmospheric pressure acting on the glass sheets increases, the spacer is urged toward the center of the unit because the air pressure in the airspace is less than the atmospheric pressure acting on the unit. When the atmospheric pressure acting on the glass sheets decreases, the spacer bows because the air pressure in the airspace is greater than the atmospheric pressure acting on the unit.
Using a breather tube of the type taught in U.S. Pat. No. 3,771,276 does not respond fast enough to equalize the air pressure in the airspace to atmospheric air pressure to prevent spacer displacement. Enlarging the hole of the breather tube for faster response to atmospheric pressure changes permits faster ingress of surrounding moisture containing air which would result in premature saturation of the desiccative spacer.
Another mechanism that is believed to cause spacer sag is temperature increases during daylight hours. As the temperature of the air in the airspace increases, e.g., due to solar heat, the air expands exerting an outward pressure on the glass sheets which increases the spaced distance between the glass sheets. The result is less resistance to spacer sag. Further, solar heat and/or radiation softens the adhesive securing the spacer to the glass sheets, and the adhesive has less resistance to spacer movement. It has been found that the adhesive securing the spacer to the glass pane is heated to temperatures of about 130.degree. F. (55.degree. C.) by solar heat and/or radiation. Spacer sag may also be caused by edge pressure of the glazing system on the marginal edge portions of the unit. In general, as the clamping pressure increases, the probability of spacer sag increases.
U.S. Pat. No. 3,868,805 teaches a double glazing unit having a spacer disposed between two panes of glass and spaced inwardly from the peripheral edges thereof to form a peripheral channel. The spacer has a T-shaped cross-sectional configuration to provide spaced recesses between the spacer and inner surface of adjacent panes. A soft and permanently deformable adhesive is applied in the recesses (1) to provide superficial adherence to the panes when the spacer is assembled therewith and (2) to aid in holding the spacer and panes in registry during assembly. Thereafter, the peripheral channel is filled with a hot resinous material to seal the joints between the spacer and panes.
The glazed unit taught in the above-mentioned patent does not eliminate spacer sag and/or spacer bow because the soft and permanently deformable adhesive does not provide sufficient structural stability to prevent spacer displacement.
U.S. Pat. No. 3,473,988 teaches a multiple glazed unit having three coextensive panes spaced apart in parallel relation by strips of polyisobutylene adhered between adjacent glass panes and spaced from the peripheral edges to form peripheral channels which are filled with a silicone elastomer. In accordance with the teachings of the above-identified patent, the polyisobutylene provides a joint that is impermeable to water vapor, and the silicone elastomer provides adhesion to hold the panes in position.
U.S. patent application Ser. No. 758,876 filed on Jan. 12, 1977, now abandoned in the names of G. H. Bowser, R. J. Mazzoni and L. F. Schutrum for "Method of Fabricating A Solar Heat Collector", which is a continuation of abandoned U.S. patent application Ser. No. 550,679, filed Feb. 18, 1975, teaches a method of fabricating a solar collector of the type having cover plates, two spacer frames and a solar radiation absorber. In general, one of the spacer frames is mounted between the cover plates and the other spacer frame is mounted between a cover plate and the absorber. The spacer frames are bonded to their respective cover plates and absorber by a preheated moisture-impervious adhesive. The above-mentioned patent application on page 8, lines 21-26, teaches that the moisture-impervious adhesive may be a silicone adhesive.
There are no teachings in the above-mentioned patent and patent application that adhesive cleats may be used to prevent spacer sag and/or spacer bow in multiple glazed units.
U.S. patent application Ser. No. 454,337 filed on Mar. 25, 1974, now patent No. 4,109,431 in the names of R. J. Mazzoni and G. H. Bowser for a "Sealing And Spacing Unit For Multiple Glazed Windows" and assigned to PPG Industries, Inc. teaches a spacing and sealing strip. The strip has a flexible dehydrator strip adhered to a flexible metal base by a layer of adhesive. Disposed on the base in a lengthwise manner are two strips of cold flowable, moisture-resistant sealant. The sealant mounts the spacing and sealing strip on the peripheral and outer marginal edge portions of glass sheets, and the dehydrator strip maintains the glass sheets in spaced relation.
Although the spacing and sealing strip of the above-identified patent application is suitable for its intended purpose, there are limitations. One of these limitations is that the dehydrator strip is secured to a flexible metal base and not adjacent glass sheets. Therefore, if the adhesive does not provide a strong enough bond between the metal base and dehydrator strip and/or if the sealant does not provide a strong enough bond between the glass sheets and metal base, spacer displacement may occur.
As can be appreciated, it would be advantageous to provide a multiple glazed unit that does not have the limitations of the prior art, e.g., spacer displacement.